1. Field of the Invention
The present invention relates to a fastening screw and a tapping screw and more particularly to a loosening prevention screw which can prevent the screw after being tightened from becoming loose and which has a reverse rotation prevention function or a locking function.
2. Description of the Prior Art
Screws are used to connect two or more members together easily, Tapping screws, in particular, have found a wide range of applications in electric appliances and automobile parts because of their advantage of not requiring female threads to be formed except for drilled holes in steel plates or resin materials.
Such screws, however, generally have a small return torque and are easily rotated in a reverse direction when subjected to vibrations after being tightened. To cope with this problem, a spring washer or a double nut is used for the bolt and nut fastenings. In the case of tapping screws, the countermeasures include a reverse rotation prevention washer and a glue.
The above-mentioned countermeasures, however, require additional parts other than the screw, such as spring washer, another nut, washer and bonding agents, raising the cost and increasing the number of work processes for fastening. In the case of the tapping screw, loosening is also caused by plastic deformation of a female screw member, not accompanied by rotation of the screw. Such a loosening cannot be prevented reliably with the above measures.